The present invention provides an apparatus and methodologies to continuously monitor, via analog to digital (A/D) sampling with an analog to digital converter, a specific transmitted signal selected for data transmission and all other radio frequency (RF) transmissions and random noise in a wireless receiver, and then utilizing this information to detect the transmitted signal, but only when this signal is of the class of direct carrier modulation specifically designed for the apparatus and methodology of this invention. Signal designs that can be used advantageously by the methods of the present invention must have both constant zero crossings of the modulated carrier frequency and be DC balanced symbols. Exemplary signal designs with these two critical properties are presented in U.S. Pat. No. 8,750,420 B2 the same inventor of the present invention, and some additional exemplary signal designs that comply with these criteria are presented in US Patent Application Publication US 2013/0034183 A1, also by this same inventor.
The receiver of the present invention A/D samples RF transmissions in the antenna, which includes the transmitted signal along with all other RF in the transmissions received by the antenna, at the zero crossings of the transmitted signal. Other RF in a receiving antenna is unwanted but inevitable. It is generally referred to as noise and interference to a transmitted signal and its relative power is commonly expressed as a signal to noise ratio. While such terminology is not strictly precise, its broad meaning is well understood. Accordingly, for purposes of this disclosure, the term “other RF” hereinafter refers to any RF energy generated by all transmitters and unintentional emitters, including random noise, that are superimposed in a receiver antenna along with the transmitted signal. Interference complicates signal detection. The novel apparatus and methods disclosed herein tolerate this interference and computationally process it to detect the signal.
Processing differs from filtering a carrier mixed with baseband content. Over a number of Hertz cycles of the transmitted carrier, filters phase cancel frequencies that are outside of the desired passband. However, filtering is not perfect in highly congested spectrum, inasmuch as some emitted radiation of differing frequencies from any source can randomly combine momentarily to appear in the passband along with the signal, thus randomly modulating the filter output waveform. However, this modulation is averaged during the demodulation of the baseband, thereby lessening its interfering effects. However, as a major advantage over the prior art, the system and processing methods of the present invention detect transmitted bits in far fewer carrier Hertz cycles than is possible with filtering. From a filtering perspective, a practical definition of interference is the RF from other transmissions and emissions that a filter is unable to remove.